This invention relates to optical fibers, and, more particularly, to the splicing of two lengths of optical fibers to form a single spliced optical fiber.
Optical fibers are strands of glass fiber processed so that light beams transmitted through the glass fiber are subject to total internal reflection. A large fraction of the incident intensity of light directed into the fiber is received at the other end of the fiber, even though the fiber may be hundreds or thousands of meters long. Optical fibers have shown great promise in communications applications, because a high density of information may be carried along the fiber. Also, the quality of the signal is less subject to external interferences of various types than are electrical signals carried on metallic wires. Moreover, the glass fibers are light in weight and made from highly plentiful substances, such as silicon dioxide.
Glass fibers are typically fabricated by preparing a cylindrical preform of glasses of two different optical indices of refraction, with a core of one glass inside a casing of a glass of slightly lower refractive index, and then processing the preform to a fiber by drawing or extruding. The optical fiber is coated with a polymer layer termed a buffer to protect the glass from scratching or other damage. The optical fibers and the buffers may be made with varying dimensions, depending upon their intended use and the manufacturer. As an example of the dimensions, in one configuration the diameter of the glass optical fiber is about 0.002-0.005 inches, and the diameter of the optical fiber plus the buffer layer is about twice the optical fiber diameter.
For some applications the optical fiber must be many kilometers long and must have a high degree of optical perfection and strength over that entire length. Preparation of an optical fiber of that length having no defects is difficult. It is therefore desirable to have the capability to splice two shorter lengths of optical fiber together to form a longer optical fiber. The need to splice optical fibers also arises when it is necessary to use a length longer than can be made from a single preform, when an existing length of fiber breaks, or when apparatus such as an amplifier is to be incorporated into a length of fiber.
The optical fiber splice must be accomplished so that there is no significant increase in loss of light in the vicinity of the splice. The spliced fiber must also have a sufficiently high strength to withstand handling in operations such as winding under tension onto a bobbin, or unwinding from the bobbin at high rates. Additionally, it must be possible to restore the buffer layer initially on the fibers being spliced.
A number of techniques for splicing optical fibers are known in the art. For example, U.S. Pat. No. 4,263,495 depicts the use of a laser to heat and fuse the ends of two opposed optical fibers. In this approach, the laser beam may be directed either perpendicular to the optical fibers, or parallel to the optical fibers and reflected to a focal point by a mirror. As such techniques were applied, they were observed to produce splices that were lacking in strength and reproducibility. As a response, automated optical fiber splicing control systems such as that of U.S. Pat. No. 5,016,971 were developed. The automated approach of U.S. Pat. No. 5,016,971 has significantly improved the ability to splice optical fibers in a reproducible manner. However, there remains the opportunity for improving the strength, optical characteristics, and reproducibility of optical fiber splices.
Therefore, there is a continuing need for an improved method for splicing optical fibers. The improved technique should produce spliced optical fibers of acceptable strength and optical performance, and have the ability to provide a continuous buffer coating over the spliced region. The splicing method should be amenable to accomplishing large numbers of splices in a reproducible manner. The present invention fulfills this need, and further provides related advantages.